Project Summary Parasitic nematodes infect over 1.5 billion humans. Control of this poverty-associated global health burden relies almost entirely on the administration of a small number of anthelmintic drugs. The prospects of anthelmintic resistance and the sub-optimal nature of these drugs in many nematode parasites demand new approaches to parasite treatment and control. However, the need to develop new antiparasitic treatment options is hampered by large gaps in our basic knowledge of the nematode biological processes that promote the establishment and maintenance of infection. Excretory-secretory (ES) products released by parasitic nematodes into their host environments are essential for host immune modulation and successful parasitism. Despite the general under- standing that the ES system is a conduit for the release of molecules (proteins and vesicles) that promote parasite survival, we have a poor understanding of the underlying structure and function of the ES apparatus in medically important parasitic nematodes. To address this gap in knowledge, this project will identify regulators of secretory function in Brugia malayi, a mosquito-transmitted ?larial nematode and causative agent of human lymphatic ?lar- iasis (LF). Recent studies in B. malayi, including on the mode of action of ivermectin, support the premise that the ES apparatus is a lucrative and unexploited source of new therapeutic targets. Our overarching hypothesis is that cell-surface receptors localized to the B. malayi ES system directly or indirectly control parasite secretory function, and that they can be targeted to interfere with the release of ES-derived molecules. We will pursue three aims, motivated by preliminary receptor leads and made feasible by innovative methods we have optimized to resolve the transcriptomic state of the B.malayi ES system and to pro?le receptors implicated in parasite se- cretory function. We focus our efforts on G protein-coupled receptors (GPCRs), which are proli?c drug targets and known to be expressed in nematode ES cells and adjacent cell types that may act on the ES system. In Aim 1, we will use innovative spatial transcriptomics approaches to resolve the transcriptome of the B. malayi ES region across intra-host stages and to identify candidate GPCRs that regulate ES function. In Aim 2, we will use reverse genetics and chemical approaches to assess the role of ES-localized GPCRs in the regulation of B. malayi secretory function. In Aim 3, we will use whole-organism model nematode and mammalian single-cell heterologous expression platforms to de?ne the pharmacology of ES-localized GPCRs and to establish functional assays for GPCR screening. Completion of this project will produce fundamental new knowledge about the ?larial nematode ES system and deliver new lead targets and validated screens for novel anti-?larial drug discovery.